In the field of graphic arts, an image-formation system with an ultra-contrast photographic characteristic (especially having a gamma value of 10 or more) is required so as to improve the reproduction of images with a continuous gradation of half-tone images or improve the reproduction of line images.
Hitherto, a particular developer, which is called a lith-developer, has been utilized for said purpose. A lith-developer contains only hydroquinone as a developing agent, where a sulfite, which is a preservative, is incorporated in the form of an adduct with formaldehyde in order not to interfere with the infectious developability thereof so that the concentration of the free sulfite ion in the developer is made extremely low (generally 0.1 mol/liter or less). Accordingly, the lith-developer is extremely easily subjected to aerial oxidation and therefore has a serious defect in that it is not durable to storage for a period of time of longer than 3 days.
As a method of obtaining a high-contrast photographic characteristic, there are methods of using a hydrazine derivative, for example, as described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857, 4,243,739, etc. According to the said methods, a high-contrast and high-sensitive photographic characteristic can be obtained and a sulfite of a high concentration can be added to the developer. As a result, the stability of the developer against aerial oxidation may remarkably be improved as compared with a lith-developer. However, when an ultra-contrast image is formed by the use of a hydrazine compound, there may be various problems of pH fluctuation by processing fatigue or aerial fatigue, as well as lowering of the density or softening of the contrast because of a decrease of the activity of the developing agent or because of accumulation of inhibitor. Accordingly, means of enhancing the hydrazine-caused hard contrast are strongly desired, and various contrast-enhancing agents have been proposed. For example, Japanese Patent Application (OPI) No. 167939/86 (the term "OPI" as used herein means a "published unexamined Japanese Patent Application") illustrates phosphonium salt compounds, Japanese Patent Application (OPI) No. 198147/86 illustrates disulfide compounds and Japanese Patent Application (OPI) No. 140340/85 illustrates amine compounds, as a contrast-enhancing agent. However, even though these compounds are used, it is still impossible to prevent the softening of the contrast of hard photographic materials during the processing thereof.
On the other hand, daylight photographic materials with low sensitivity can be obtained by the use of a hydrazine compound. For example, Japanese Patent Application (OPI) Nos. 83038/85 and 162246/85 illustrate water-soluble rhodium salt-containing silver halide photographic materials. However, when a sufficient amount of rhodium for lowering the sensitivity is added, the contrast enhancement by the hydrazine compound is thereby inhibited so that a desired sufficiently high contrast image can not be obtained.
Japanese Patent Application (OPI) No. 157633/84 mentions a method of preparing a silver halide photographic material which contains a water-soluble rhodium salt in an amount of from 10.sup.-8 to 10.sup.-5 mol per mol of silver halide and an organic desensitizing agent having a positive sum of anode potential and cathode potential by polarography. However, according to the method, although the sensitivity can be lowered, it is impossible to obtain a sufficiently high contrast image for practical use in the industrial field.
Japanese Patent Application (OPI) No. 62245/81 discloses a method of forming a high contrast image in which the development is conducted in the presence of tetrazolium compound so that the development in the part of the toe of the characteristic curve is inhibited by the tetrazolium compound. However, the tetrazolium compound-containing silver halide photographic material has some problems in that the material deteriorates during storage so that only a soft image can be obtained and the reaction product of the tetrazolium compound by development partly remains in the film so as to cause film-staining or development unevenness.
Thus, the method of increasing the contrast of photographic materials by the use of a hydrazine compound is always accompanied by the problem of the softening of the contrast thereof, and for example, the contrast would often soften during a running processing operation or by addition of a rhodium salt and/or an organic desensitizing agent so as to obtain a low sensitive image. That is, it is extremely difficult to desensitize the ultra-contrast image formed by the use of a hydrazine compound while maintaining the high contrast of the image.
As the case may be, a large amount of a hydrazine compound is often added so as to attain the high contrast. As a result, the strength of the emulsion film is weakened, the storage stability is worsened or a noticeably amount of the hydrazine compound is released into the developer during the running processing operation so that the processing solution is stained by the hydrazine compound or the photographic material processed is badly affected by the compound. Accordingly, a method of accelerating the high contrast of photographic materials by the use of a small amount of a hydrazine compound is also desired.
As mentioned above, it is extremely difficult to lower the sensitivity of the photographic material which has been made high in contrast by addition of a hydrazine compound while maintaining the high contrast of the material. This is because of the following reasons: The hydrazine compound participates in the development of the photographic material so as to induce nucleating infectious development, by the electron-donating capacity thereof, to silver halide to thereby give a high contrast image, while the organic desensitizing agent or inorganic desensitizing agent, such as rhodium salts, is a photoelectroreceptor. This has a function of receiving a photoelectron during image exposure to prevent latent image formation, thereby lowering the sensitivity of the photographic material. On the other hand, the desensitizing agent can receive the electrons as donated by the electron-donating agent, such as hydrazine compounds, so as to inhibit nucleating infectious development by the agent and, as a result, a high contrast image can not be obtained. Accordingly, a method of desensitizing a high contrast photographic material containing a hydrazine compound while maintaining the high contrast of the material is strongly desired.
In the reversing step field of graphic arts, a photographic light-sensitive material having a photographic characteristic with a gradation of a gamma value of from 4 to 8 or so is used in addition to the photographic material with an ultra-contrast contrast gradation (gamma value of 10 or more). The former photographic material with such a gradation has less problems of pin holes because of dust and white spots (tape-adhered spots) due to adhesive tapes applied for fixation of an original thereto, than the latter ultra-contrast photographic material, during contact the reversing step. On the other hand, the former has a defect in that the sharpness of letters or half-tone images to be formed thereon is inferior to that of images to be formed on the latter. For practical use, it is necessary to keep an image sharpness of some degree, and for this, the gamma value is required to fall within the range of from 3.5 to 8 or so. For daylight room use, the sensitivity of the photographic materials is required to be lowered. It may be possible to lower the sensitivity by incorporation of a rhodium salt into the silver halide grains in the photographic material. However, this lowers the gamma value of the material so that the image sharpness thereof is lost. When a dye is used for lowering the sensitivity, the anti-irradiation effect of the dye causes another problem in that the tone adjustment of the half-tone images or the line width adjustment of the linear images in accordance with the exposure amount becomes difficult.
Accordingly, a method of lowering only the sensitivity without lowering the gamma value is strongly desired.
For reversal photographic materials, the processed film is used as an original and subjected to contact printing with an Hg printer, or is printed to a printing plate such as PS plate with an ultraviolet ray in the post-step. Accordingly, these are required to have a high ultraviolet density, or on the contrary, there is a desire to reduce the amount of the silver to be coated thereon as little as possible for the purpose of economizing the natural resources. Under the circumstances, a method of obtaining a higher ultraviolet density with a reduced silver amount coated is strongly desired.
In order to overcome the above-mentioned problems, a method of using fine silver halide grains consisting essentially of silver chloride was found effective. However, this method has the following problems.
Cubic silver chlorobromide or silver chloride grains having a mean grain size of more than 0.15.mu. and containing 99 mol % or more AgCl have too high a sensitivity for a daylight photographic material. When a rhodium salt is added, the Dmax is difficult to appear; and when a nucleating agent is added, the nucleating development is difficult to proceed. Anyhow, these systems are defective since the contrast is soft.
Japanese Patent Application (OPI) No. 140338/85 mentions a method of using silver halide grains having a mean grain size of 0.15.mu. or less, but it is silent about cubic silver chlorobromide or silver chloride grains having a mean grain size of 0.15.mu. or less and containing 99 mol % or more silver chloride. This is because such cubic grains have a high solubility and therefore are difficult to prepare.
Silver chlorobromide grains containing bromine in an amount of 2 mol % or more, even having a mean grain size of 0.15.mu. or less, have a defect in that the grains are often fogged with ease when processed in the presence of a UV-cut fluorescent light or a white fluorescent light because of the prolonged long wavelength edge of the absorption wavelength.
Spherical or roundish grains having a mean grain size of 0.15.mu. or less and containing 99 mol % or more AgCl have a defect in that the contrast is often softened when a large amount of rhodium is added to the system of the grains to which a nucleating agent has been added so as to lower the sensitivity thereof.
For silver chlorobromide or silver chloride grains having a mean grain size of 0.15.mu. or less and containing bromine in an amount of 1% or less, there is not known any method for stably preparing the grains since the grains have a high solubility.
In particular, silver halide grains consisting essentially of silver chloride and having a mean grain size of 0.15.mu. or less have a high solubility. Therefore, when the grains are prepared, the temperature for grain formation is lowered or the speed of adding raw material components is accelerated so as to minimize the grain size. However, even under such grain formation conditions, the grains are often forced to be physically ripened during the grain formation or after the grain formation and, in particular, the grain size becomes large or the grains are deformed in the subsequent desalting step (flocculation, and rinsing-in-water step) or in the post-ripening step thereafter. Such is defective and problematic. When the grain formation is conducted under the condition of a temperature of 30.degree. C. or less, the temperature is hardly controlled to be constant in view of the manufacture operation of the grains. Accordingly, a method capable of stably preparing the grains is desired.
In the preparation of fine cubic-silver chloride grains, the grain size fluctuation is noticeable after the formation of the grains or in the subsequent desalting step or in the post-ripening step. In order to prevent such grain size fluctuation, a compound capable of adsorbing to the surface of the silver halide grains may be added as a grain growth inhibitor. Although the grain size fluctuation is somewhat inhibited by the addition of such an inhibitor, the crystal habit of the resulting grains problematically varies. Accordingly, a method capable of preparing silver halide grains while maintaining the size and the crystal habit (cubic crystal) is desired.
On the other hand, the grain growth inhibitor is generally a compound which is called an antifoggant or stabilizer. Therefore, when silver halide grains are prepared in the presence of the inhibitor and the inhibitor still remains in the resulting emulsion after rinsing-in-water, the successive chemical ripening with a chemical sensitizer in the post-ripening step is extremely retarded because of the inhibitor remaining in the emulsion, or the photographic sensitivity or Dmax is lowered to a degree of no practical use, or the adsorption of the spectral sensitizing dye to the emulsion is extremely retarded. Such are serious problems and so means of overcoming these problems are earnestly desired.
Silver chloride grains having a mean grain size of 0.15.mu. have a problem in that they often cause development unevenness in the development step. In particular, roller-squeezing unevenness in the development part in an automatic developing machine is one great problem. This is considered also because of the high solubility of the grains. The phenomenon is extremely remarkable in a fine silver chloride grain emulsion. Accordingly, means of overcoming such problematic phenomenon are strongly desired.
When a prepared stock emulsion is stored in a refrigerator for a long period of time, the grain size is often enlarged or the grains are often deformed in the case of silver halide grains having a mean grain size of 0.15.mu. or less and containing 99 mol % or more silver chloride. Accordingly, there is a great problem in the storage stability of the stock emulsion of the silver halide grains.
When the stock emulsion is dissolved and then stored for a long period of time (2 to 10 hours) in the state of a coating solution as dissolved, the grains in the resulting solution are physically ripened so that the grain size becomes large and the grains are deformed. Thus, the photographic property of the coating solution varies. These are serious problems.
Anyhow, the silver halide grains having a mean grain size of 0.15.mu. or less and containing 99 mol % or more silver chloride have various problems in that the grain size is enlarged or the grains are deformed because of the extremely high solubility of the grains. Therefore, means of overcoming these problems are strongly desired.